Rachel Pelkey has seen it many times before. Working behind the counter at Grille Zone in Boston, she'll watch diners finish their meal, gather their rubbish, march it to the front of the restaurant, and then look confused.

"The biggest question I get is 'Where's the garbage?' " she says with the kind of grin a mother gives her questioning child. "I explain that we don't have a garbage can, only compost and recycling."

That often sparks a chain of follow-up questions: Why only compost? What do you mean it's a near zero-waste restaurant? Everything is biodegradable? Even the plates and knives?

Once customers catch on, they get kind of excited, she says. "They like being a part of something so green," says Ms. Pelkey. "Yeah, we serve burgers and fries, but we're also as environmentally friendly as they come."

As more Americans seek out products with green credentials, more quick and casual restaurants are ready to serve them. Eating green no longer means just ordering from a vegetarian menu. In fact, it doesn't even have to mean eating healthy.

"For a restaurant to be truly green, they have to think about the lighting, the napkins, the cleaning products, the waste, the grill – everything," says Michael Oshman, founder of the Green Restaurant Association (GRA), a national, nonprofit consultancy in Boston that helps eateries become more environmentally friendly. "But what a lot of restaurateurs don't realize is that taking the necessary steps is not only good for the environment and good for their image, it's also a way to lower costs."

Thanks to improved technology and increased adoption of sustainable products, even burger joints can go green.